Resistor Calculator

Reading the Rainbow: A Guide to the Resistor Color Code

A resistor is a fundamental passive electrical component that creates resistance in the flow of electric current. In virtually all electronic circuits, resistors are used to control current levels, divide voltages, and provide bias to active components like transistors. Through-hole resistors, the small cylindrical components with wires coming out of each end, are often too small to have their resistance value printed on them directly. Instead, they use a standardized system of colored bands to indicate their resistance value and tolerance.

This resistor color code calculator is an essential utility for anyone working with electronics, from students learning the basics to experienced hobbyists and technicians building or troubleshooting circuits. It provides a simple, interactive way to decode these colored bands. By selecting the colors for each band, the calculator instantly displays the resistor's value in Ohms (Ω), along with its tolerance, which indicates the acceptable range of variation from its stated value. This tool eliminates the need to memorize the color code system and prevents misreading, ensuring you select the correct component for your circuit every time.

How to Read Resistor Color Codes

The color code is a standardized system where each color corresponds to a number, a multiplier, or a tolerance value. The system is read from left to right, with the tolerance band typically being gold or silver and positioned at the far right.

4-Band Resistors

• Band 1: First significant digit of the resistance value.
• Band 2: Second significant digit of the resistance value.
• Band 3 (Multiplier): The power of 10 to multiply the first two digits by.
• Band 4 (Tolerance): Indicates the permissible tolerance in the resistance value (e.g., Gold is ±5%).

Example: A resistor has the bands Brown, Black, Orange, Gold.
• Brown = 1
• Black = 0
• Orange (Multiplier) = ×10³ or ×1,000
• Gold (Tolerance) = ±5%
The value is 10 × 1,000 = 10,000 Ω, or 10 kΩ, with a ±5% tolerance.

5-Band Resistors (High Precision)

High-precision resistors use a 5-band system for greater accuracy.

• Band 1: First significant digit.
• Band 2: Second significant digit.
• Band 3: Third significant digit.
• Band 4 (Multiplier): The power of 10 multiplier.
• Band 5 (Tolerance): The tolerance band (often brown or red for precision resistors).

Example: A resistor has the bands Red, Violet, Green, Red, Brown.
• Red = 2
• Violet = 7
• Green = 5
• Red (Multiplier) = ×10² or ×100
• Brown (Tolerance) = ±1%
The value is 275 × 100 = 27,500 Ω, or 27.5 kΩ, with a ±1% tolerance.